1. Field of the Invention
The invention relates to a method of manufacturing a semiconductor device and, more particularly, to a semiconductor device having a gold bump for an electrode constituting an external connecting terminal
2. Description of the Prior Art
Many proposals have conventionally been made for methods of manufacturing a gold bump for an electrode of a semiconductor device. FIGS. 6 are a cross-sectional view showing the steps of a conventional manufacturing process for a gold bump for an electrode.
Conventionally, as shown in FIG. 6a, an A1 electrode pad 62 and a passivation film 63 are formed on an integrated circuit 61. Then, as shown in FIG. 6b, a Ti film layer 64 having a thickness of 0.1 .mu.m and a pt film layer 65 having a thickness of 0.2 .mu.m is formed over the entire surface of integrated circuit 61 by sputtering or deposition. Thereafter, as shown in FIG. 6c, a photoresist film layer 66 is formed above pad 62 to a thickness of 1 .mu.m by using a positive or negative resist. The unnecessary portion of the Pt film layer 65 is next removed by wet etching using aqua regia (a mixed solution of hydrochloric acid and nitric acid) and using layer 66 as a mask. After removing the photoresist film layer 66 by a remover or an oxygen-plasma method, a photoresist film layer 67 is formed to a thickness of 3 .mu.m by using a positive or negative resist in such a manner as to have an opening portion on the patterned Pt film layer 65, as shown in FIG. 6e. A bump electrode 68 is formed by Au electrolytic plating while using the photoresist film layer 67 as a mask, and using the Ti film layer 64 as a conductive film for electrolytic plating. The photoresist film 67 is then removed by a remover or an oxygen-plasma method, leaving the structure shown in FIG. 6f. Finally, the unnecessary portion of the Ti film layer 64 is removed by using a mixed solution of ammonia water and aqueous hydrogen peroxide while using the patterned Pt film layer 65 as a mask, resulting in the structure shown in FIG. 6g.
This conventional manufacturing method has the following drawbacks.
Firstly, since photoresist film layer 66 is used as an etching mask for Pt film layer 65, two photo processes, including a photo process for Au plating, are required.
Secondly, since bump electrode 68 formed by Au plating must be adhered to Pt film layer 65, which metal is different from Au, the strength of the adhesive bond is so low that its reliability is insufficient when bump electrode 68 is mounted on a semiconductor device. Ti thin film 64 is used as the conductive film for Au plating. Since a Ti surface is readily oxidized, a contact failure is apt to be caused at the contact point, and since the Ti film is thin, the conductive film is sometimes broken at the stepped portion on the surface of the integrated circuit.
In addition, since there is no step of etching the surface of the bump electrode 68, when the bump electrode 68 is mounted on a semiconductor device, a large electric resistance is caused between the bump electrode and the substrate by the adhesion of a residue of the photoresist film 67 or the like.